Field of the Invention
This invention relates to a method for producing a breathable film based on polyvinyl chloride (PVC).
Discussion of Related Art
PVC-based films are used, for example, in the production of imitation leathers, in which as a rule, a composite of textile and glass or carbon fiber weaves, knits, polymer foams or nonwovens is provided with a coating of a PVC film of this kind. Depending on the application, these coatings can be embodied as compact or foamed and can have a grained surface provided, for example, by stamping so that they correspond to a leather structure.
If the PVC-based film is to have breathable properties, which is advantageous, for example, in a seat cover or in shoe uppers as well as in wall and ceiling coverings in order to permit water vapor to pass through, then the film must have a sufficient number of pores through which the water vapor can pass.
In the prior art, it is known to take inherently non-breathable PVC-based films and make them breathable, for example by needling, such as the pores are mechanically produced.
German Patent Reference DE 1 960 992 A1 discloses producing a breathable, microporous film material made of a polymer mixture including polyurethane elastomers and polyvinyl chloride, and the polymer is dissolved in an organic solvent, applied in a thin layer to a substrate whose substrate surface is wetted with a precipitating agent and the underside of the thus coated substrate is brought into contact with a porous support, which is for its part also wetted with a precipitating agent, until the polymer has precipitated on the surface of the substrate in the form of a microporous layer that is essentially free of macro-cavities. The known method is therefore not only extremely complex in terms of equipment and not very efficient, but also appears to be in need of improvement from the standpoint of health and environmental protection due to its preferred use of the solvent dimethylformamide.